Flotation process and apparatus



June 6, 1933. FQRRESTER 1,912,630

FLOA'IATION PROCESS AND APPARATUS Filed June 8, 1928 2 Sheets-Sheet lJune 6, 1933. D. FORRESTER I FLOATATION PROCESS AND APPARATUS PatentedJune 6, 1933 UNITED STATES PATENT OFFICE DAVID LAWTON FORRESTER, OFGLOBE, ARIZONA, ASSIGNOR 1'0 MATLESS CELL LATENT HOLDING CORPORATION, ACORPORATION OF ARIZONA 4 r'nom'rron rnocrss AND urmarus Applicationfiled June a, 1928. Serial No. 283,781.

rocky constituents thereof. By this inven-' tion the pulp is aerated soas to produce bubbles of efiective flotation size in sufliclent quantityto persist efl'ectively throughout the operation of separation andconcentration of the particles to be floated; the aerated pulp may beintroduced from the agitation chamber into the separation chambersubstantlally throughout its entire depth; and current-s and eddies areset up in the separation chamber by which the entire volume of pulp inthe separation chamber is impre ated with a plenum of flotation bubbles,a ording opportunity for repeated contact between flotation bubbles andparticles to be, floated. At the same time the intercommunicatingagitation chamber and separation chamberare so arranged that there aremaintained simultaneously a pulp in violent agitation in the agitationchamber, and in the separation chamber currents and eddies of pulppositive and\d'istinct enoughto assure required dissemination offlotation bubbles and particles to be float- 5 ed throughout the entirevolume of pulp in the separation chamber, but at the same time mild andgentle enongh to permit the formation of the desired froth.

By the resent invention certain improvements in otation method and aparatus are provided which by simplicity 0 operation and constructionafford better metallurgical results and reduce the cost of production,in: stallation and operation.

The prior-art indicates that the requirements of the effective bubblecolumn apparatus and method have been supplied in the past byintroducing air through a porous medium, e. g. canvas, blanket, or aporous 50 solid, perforated pipe, etc., or by introducing bubbles, ofefi'ecti've flotation size from the air by a mechanically operatedimpeller which beat air into the pulp in an agitation chamber, eitherfrom the open atmosphere in the agitation chamber or from air supplied.under pressure through the bottom of the agitation chamber, or bycascading or splashing streams or bodies of pulp into a mass of pulp inthe fashion of a waterfall. These three methods of air introduction anddispersion are known respectively as pneumatic, centrifugal, and cascadeor plunging stream methods.

In the early commercial pneumatic flotation machine andmethod, theaeration, agitation, and circulation were produced by passing the air atarelatively high pressure through a porous medium. In this manner theair is introduced in a finely divided state into the pulp from below.The minute air moment of introduction into the pulp, produce someagitation of the pulp efi'ective aeration of the pulp, and a circulationby displacement of the pulp within the cell, resultmg in the formationof a mineral bearing froth on the surface of the pulp. This method hascertain apparent disadvantages in practice, the more important of whichare the high power costs, high repair and operation costs in keeping theporous medium clean, loss of efficiency in the entire or partialblinding of the porous medium, loss of efliciency in performing thefunctions of agitation and separation in the same chamber, loss ofefliciency in necessary restriction of volume of air admitted so as tomaintain agitation sulficiently mild to permit froth formation. Thereare not present the currents and eddies of pulp essential to the mosteificient operation. 4 In the centrifugal method, aeration, agitationand circulation are produced by a mechanically rotated impeller whichbeats air into the pulp in an agitation chamber, either from the openatmosphere in the agitation chamber or from air supplied under pressurethrough the bottom of the agitation chamber and causes the pulp tocirculate from top of the agitation chamber into the separation chamberdown through the separation chamber and back into the agitation chamberat the bottom thereof. The main disadvantages of this method are,original cost of installation, cost of power and repair, and want ofthorough consistent impregnation of the entire volume of pulp in theseparation chamber so that the'pulp falls back upon itself and on to themass of pulp in the separation.

chamber. The theory is, that the cascading of the pulp entrains air forthe purpose of providing the requisite bubbles of efiective flotationsize. The main disadvantages of the cascade method are that suflicientair is not entrained in the pulp for most eflective flotation, nor arethe proper currents produced and maintained in the separation chambersfor the thorough and proper impregnation of the pulp in the separationchambers with bubbles of effective flotation sizes permitting theformation of an etficient mineral bearing froth.

The invention may be understood from the description in connection withthe accompanying drawings in which Fig. 1 is a longitudinal sectionthrough an illustrative embodiment of the invention; Fig. 2 is asecdicates the bottom of a flotation cell that tion along the line 2-2of Fig. 1; Figs. 3, 4 and 5 are sections similar to Fig. 2 showingmodifications; Fig. 6 is a plan view of another modification; and Fig. 7is a section along-the line 77 of Fig. 6.

In the drawings reference character 1 inmay be horizontal or may be madeto slope from the inlet to the outlet at the end of the cell. The cellis provided with side walls 2 which slope upwardly and outwardly .fromthe bottom. The vertical side walls 3 extend from the upper edges of thesloping walls 2 and are of such a height that the froth that is formedflows over the upper edges of the walls 3 into the launders 4 for theconcentrate. The end walls 5 of the cell proper extend entirely acrossthe same.

Vertically disposed partitions 6 extend from one end of the cell to theother, and are so located that their upper edges extend some distanceabove the normal liquid level in the cell, and high enough to preventsplash over the top from the agitation chamber into the separationchamber. The lower edges of the partition 6 may terminate either nearthe liquid level or may extend a considerable distance below the normalliquid level. The lower portions of the partition 6 in the froth andliquid zones may be provided with holes or openings 6 through which theliquid may flow. The greater distance the partition 6 extends below thepulp essentialwhich also extend from the front end wall 5 to the rearend wall 5 of the cell. These lpO)(.':.rtitions are shown in Figs. 1 and2 as ing inclined outwardly and downwardly with their upper edgesextending some distance above the lower edges of the partitions 6.Deflecting strips 7 may be provided along the outer sides of thepartitions 7 to aid in directing the flow of the liquid.

A rowof open-ended pipes 8 extends into the lower portion of the celland these pipes are connected to the air manifold 9 through which airunder pressure can be forced into the liquid to agitate the same.

An inlet compartment 10 is located at one end of the cell and an opening11 is provided 'in the end wall 5 through which the pulp that isintroduced into the compartment 10 can enter the cell proper. An opening12 is provided in the lower portion of the rear end wall 5 through whichthe tailings pass into the outlet compartment 13. An adjustable weirdischarge14 is provided for the outlet compartment 13 over which thetailings flow and by which the pulp level in the cell can be regulated.The tailings after flowing over the weir 14, then finally pass outthrough the opening 15. v

The operation is as follows: Air is introduced through the pipes 8 at asufficient distance below the level of the pulp to cause violentagitation of the same, the formation of sufiicient bubbles of effectiveflotation size, and inducement of the required currents and eddies ofpulp in the separation chambers. The pipes may be about three-quartersof an inch in diameter so that large bubbles of air escape from the pipeand rise upwardly through the liquid. These bubbles and downward crossand counter currents of the pulp are created with the result that thelarge bubbles of air are rapidly and thoroughly broken up and dispersedinto numerous small bubbles of efl'ective flotation size. These smallbubbles of efi'ective flotation size are suflicient in quantity andpersist for a suflicient length of time to permit the same to beefliciently disseminated throughout the pulp and cause flotation of themineral particles to take place as desired.

The continuous entrance of the large bubbles and the consequentagitation of the pulp and its thorough impregnation with air cause thepulp to assume a higher hydrostatic head over a considerable area abovethe points of entry of the air, than in the remainder of @the walls 3-and 2 and again upwardly between the partitions 7. The aerated pulpflows into the compartments outside of the L partitions 6 from thecompartment between those partitions not only through the holes 6' andunder the edges of the partitions 6, but also for substantially theentire depth below the partitions 6. In this way currents and eddiesrequired for eflicient dissemination of the bubbles and pulp in theseparation chambers between the partitions 6 and the walls 3 are set up,thus throwing out into the body of pulp in the separation chambers avery large number of bubbles of effective flotation size which risethrough the pulp in the'separation chambers to the surface, thus formingthe mineral bearing froth which flows over the upper edges of the walls3 into the launders 4. In this way the currents and eddies of pulp inthe separation chambers so impregnate and saturate the pulp with thebubbles of effective flotation size that repeated contact between thesebubbles and particles of mineral to be floated takes place throughoutthe volume of pulp in the separation chambers before the pulp carried inthe downward current near the walls 3 and. 2 re-enters the currentpassing upwardly between the partitions 7 The rapidity of flow of theaerated pulp fromthe chamber between the partitions 6 to the chambersoutside of these partitions'may be controlled by the difference inhydrostatic head between the chambers, by the adjustments of thepartitions 6 and 7 and also by adjusting the normal pulp level in thecell by means of the overflow weir 14. The difference in hydrostatichead may be regulated by the amount of air introduced through the pipe 8in large bubbles or by the pulp level in the cell.

- By the arrangement above described, there is procured a violentagitation in the space above the ends of the pipe and to each sidethereof, and at the same time the induced currents and eddies whichenter the separation chambers are mild and gentle enough to permit theformation of the mineral bearin froth and are positive and distinctenough to bring about the required dissemination of bubbles and mineralparticles in the entire volume of pulp in the separation chambers.

It has been found that with this invention there isconcentrationprogress throughout'the depth of the separation chambers, the percentageof content of the mineral to be floated increasing from the bottom tothe top of the pulp in the separation chamber. Air at low pressure andin suflicient volume is introduced in large bubbles so that thedisadvantages that occur when porous media and mechanical aerators andagitators are used are eliminated.

By providing the'large number of bubbles of effective flotation size andtransferring them to the separation chambers, as above described, it ispossible to o erate the process with varying levels of pu pin the celland with practically any level of pulp, which may be varied to suit theparticular ore that is being treated.

By this invention primary flotation may be carried out in which the moreeasily floated minerals are treated and a clean concentrate is desiredin one operation, or secondary flotation may be carried out following aprimary flotation so as to separate the more refractory mineralparticles which escape the primary. treatment, thus producing a lowgrade concentrate, or a cleaning flotation can be carried out for thepurpose of cleaning low grade concentrates from the secondary flotationor for recleaning all concentrates. In any of these flotationoperations, the aeration is effectively produced by the entering airbubbles and the pulp is saturated with bubbles of effective flotationsize. When primary flotation is being carried on the currents and eddiesmay be. less pronounced and vigorous; when the cleaning flotation isbeing carried on the currents and eddies may be least pronounced andvigorous; and when the secondary flotation is being carried on thecurrents and eddies should be most pronounced and vigorous.

The process can be used for carrying on different sorts of flotationmerely by regulating the quantity of air that is introduced .or byraising or lowering the pulp level in the cell so as to produce thedesired intensity of currents and eddies for the best results.

In the modification shown in Fig. 3, the strips'7 are left off of thepartitions 7 and the upper edges of the partitions 7 are shown as beinglocated approximately at the same level as the lower edges of thepartitions 6.

The operation is similar to that already describe 1 In the modificationshown in Fig. 4, the partitions 7 are omitted entirely and the loweredges of the partitions 6 terminate near the pulp level and have noopenings therethrough. The partitions 6 in all the modifications may bemade sufliciently high to prevent the pulp from splashing over the u eredges thereof or a hood 16, as shown 4, may be provided for thispurpose.

In the partitions 7 are located some distance apart modification shownin Fig. 5, the.

on opposite sides of pipes 8 and are shown as being installed parallelto each other. In this modification the upper edges of the partitions 7extend some considerable distance above the normal pulp level so thatthe pulp agitated and aerated by the incoming air flows over the upperedges of the partitions 7. After the aerated pulp drops over the edgesof the partition 7, it then passes under the lower edges of thepartitions 6, or through the holes 6' in a manner similar to thatalready described. The arrangement of the partitions 7 as shown in Fig.5 is advantageous in certain operations, particularly where a primaryflotation or roughing operation is desired. The dropping of the pulpover the upper edges of the partitions 7 is not for the purpose ofentrapping or entraining air in the pulp for flotation purposes, sincethe pulp has already'been saturated with bubbles of effective flotationsize prior to its drop over the partitions 7. This action seems incertain instances to aid in disseminating the bubbles of effectiveflotation size that have already been produced by the agitation of therising air from the pipes 8. a

In the modification shown in Figs. 6 and 7 the cell is shown as acircular one with a circular bottom 21, conical wall 22 and acylindrical wall 23. An annular launder 24 is provided around thecircular wall 23 and an lar partition 26 that performs a functionsimilar to the partitions 6 already described, is located within thecircular wall 23 and may be provided with openings 26' along the lowerportion thereof in the froth and liquid zones. An air pipe 28 extendsdown inside the partition 26 and its lower open end terminates at asufiicient distance below the pulp level to provide eflicient agitationand formation of suflicient bubbles of effective flotation size and toinduce the required currents and edof pipes 28 may be used for the samepurpose.

The mineral' pulp may be introduced into the cell and the tailingsdischarged therefrom as is ordinarily done in cells of this type Theoperation of the modification s own in Figs. 6 and 7 is similar to thatal- Ieady described in connection with the other res. 'l he location ofthe partitions 6 or the partition 26 should be approximately at the lineof demarcation between the portion. of the liquid that is raised by'theair bubbles and the remainder of the surface area of the cell. This areais convex, and is, ina cell of a commercial size, about 20 or 22 incheswide and extends from one end of the cell to the other with a row of airinlet pipes 8, as indicated in Figs. 1 to 5. This area is, of course,circular-in the modification shown'in Figs. 6 and 7 and is approximately20 inches in dierate satisfactorily without the partitions 7,

but in certain instances the partitions 7 have some advantages.

The following is given as a specific example of a cell operated and madein accordance with this invention, but it is to be understood thatdimensions may be altered and variations and modifications can be madewithout departing from the invention: A cell similar to thosedescribed-in connection with Figs. 1 to 5 may be made 4 feet wide and 50feet long with the air pipes 8 extending about 2 feet below the level ofthe pulp. The'partitions 6 may be placed about 22 inches apart andhavetheir lower edges terminating near the pulp level "or the loweredges may extend downwardly several inches into the pulp. The usualflotation agents-may be used with mineral pulp and the air may beintroduced at about 1 lbs. pressure through pipes of aboutthree-quarters inch in diameter placed approximately 5 inches apart.

I claim:

1. The process of concentrating ore or other substances by flotationwhich comprises introduc'ing air in large bubbles into a pulp in anunobstructed space near the middle of a cell at a suflicient distancebelow the surface thereof to aerate the pulp and provide enough bubblesof effective flotation size for flotation, segregating the surface areaof the pulp above the point where the air is introduced from the areaoutside of it, and passing the aerated pulp into the space below saidlastnamed area throughout substantially the entire depth of said spaceand also substantially vertically below the outer edges of said space. v

2. The process of concentratingore or other substances by flotationwhich comprises introducing air in large bubbles into a pulp in anunobstructed space near the middle of a cell along a row of points at asuflicientdistance below the surface thereof to aerate the pulp andprovide enough bubbles of effective flotation size for flotation,segregating the surface area of the pulp above the point where the airin introduced from the area outside of it, and passing the aerated pulpinto the space below said last-named area throughout substantially theentire depth of said space and also substantially vertically below theouter edges of saidspace.

3. In a flotation apparatus for ore concentration, a cell, means forintroducing air in-large bubbles into an unobstructed space in said cellbelow the normal liquid level therein in suificient quantity to causeviolent agitation, partitions to separate the surface area of the liquidin said cell that is violently agitated by introducing the air from there- Inainder of the surface area, said partitions extending only a shortdistance below the normal liquid level, and partitions convergingupwardly below and between said first named partitions.

4. In a flotation apparatus for ore concentration, a cell, means forintroducing air in large bubbles into an unobstructed space in said cellbelow the normal liquid level therein in suflicient quantity to causeviolent agitation, means comprising partitions to separate the surfacearea of the liquid in said cell that is violently agitated byintroducing the air from the remainder of the surface area, and

- separate partitions located at a lower level than said first-namedpartitions with .unobstructed spaces between the lower edges of saidfirst named partitions and the upper edges of said last namedpartitions.

DAVID LAWTON FORRESTER.

